This is my first OOP php app and I'm getting a little stumped here...

I created the following class that extends the CI_Model

class LXCoreModel extends CI_Model
{
    function __construct()
    {
             parent::__construct();
    }

    public function elementExists($table, $row, $data)
    {
         $result = $this->db
             ->select('*')
             ->from($table)
             ->where($row, $data)
             ->get()
             ->result();
         if (empty($result))
             return false;
         return true;
    }
}

And here is the class extending the class above:

class LXAccAdminModel extends LXCoreModel
{
    function __construct()
    {
        parent::__construct();
    }

    function addAccountStatus($statusId = NULL, $username = NULL)
    {
        if ($statusId == NULL)
            $statusId = $this->input->post('accountStatusId');
        if ($username == NULL)
            $username = $this->input->post('username');

        if (elementExists('accounts', 'username', $username))
            if (elementExists('statuses', 'id', $statusId)) {
               $this->db
                   ->insert('accountstatus', array(
                       'statusid' => $statusId,
                       'username' => $username
                   ));
               return true;
            }
        return false;
    }
}

Both classes are in the CI_Model directory, and the class LXCoreModel is autoloaded (the line $autoload['model'] = array('LXCoreModel'); exists in the autoload.php file) and yet, when I try to run my code I get this error:

Fatal error: Call to undefined function elementExists() in C:\wamp\www\CI_APP\application\models\LXAccAdminModel.php on line 25